In Mr. Davidson's 8th grade class, there are 7 more male students than female students. If 2/3 of the students are male, how many students are in the class?
Let there be $x$ students in the class. $\frac{2}{3}x$ students are male and $\frac{1}{3}x$ students are female. We have $\frac{2}{3}x = \frac{1}{3}x + 7$, so $\frac{1}{3}x = 7 \Rightarrow x = \boxed{21}$ students.